College of LAS « Illinois

Astronomy

Researchers Detect 'Near Miss' Supernova Explosion

supernova

Nearly a decade ago, University of Illinois astronomers said that a supernova star might have left detectable evidence on the Earth of a "near miss" explosion. Today, new findings show they were right.

All stars die, but only 1 percent of them do so in a spectacular supernova explosion, says Brian Fields, LAS astronomer. He calls supernovae the "James Dean of stars." They are huge stars that live fast and die young.

With a mass more than about eight times that of the Sun, a star doomed to die as a supernova struggles to maintain stability against its own gravity. It eventually collapses under its own weight, resulting in a powerful explosion whose brilliance is brighter than one billion suns.  A supernova ejects material at velocities reaching 5 to 10 percent the speed of light.  And if it's close enough, this material could be deposited on Earth.

Back in 1996, Fields and his colleagues theorized that a supernova explosion close to Earth would leave behind a tell-tale signature, such as radioactive atoms. Sure enough, just one year later researchers at Germany's Technical University emailed Fields to inform him that they discovered radioactive iron-60 in the crust of deep-sea rocks in the Pacific Ocean.

Now, the Germans have found evidence of radioactive iron in a different sample of ocean rocks—in layers that point even more directly to a supernova source.

"Until the new German results came out in 2004, this whole thing has been more of a hobby for me," says Fields. "But with the new data, this is serious."

In fact, the latest findings have spurred interest among other groups across the world. Now, the search is on for additional radioactive materials, which might have been deposited on Earth by a supernova explosion. In a recently published paper, Fields and his colleagues have even come up with a "wish list" of elements to hunt for.

Researchers estimate that this particular supernova explosion occurred 3 million years ago at a distance of about 100 light years away. For a supernova explosion to endanger Earth, it would have to be within 30 light years.  And according to Fields, no massive stars within that range are threatening to explode.

"So don't lose any sleep over this," he says. "There are things in the world to worry about, but this isn't one of them."

Fall/Winter 2005–06